1. Field of the Invention
The present invention relates to a discrete semiconductor device. More particularly, it relates to a discrete semiconductor device for small signal operation having excellent high-frequency characteristics and heat dissipation performance.
2. Description of the Related Art
A discrete semiconductor device of the prior art is typically packaged in a DIP (dual inline package) shown in FIG. 25. FIG. 25A is a cut-away view from above of a resin-sealed DIP, and FIG. 25B is a cut-away view of the side of the resin-sealed DIP. In the drawing, numeral 2 denotes a sealing resin, 8 denotes a discrete semiconductor element, 9 denotes a wire connecting an electrode of the discrete semiconductor element 8 and an inner lead 39, 38 denotes an island for securing the discrete semiconductor element 8, 39 denotes the inner lead and 40 denotes an outer lead.
In the case of such a resin-molded DIP, the discrete semiconductor element 8 is secured onto the island 38 of a lead frame 41 by die bonding and the electrode of the discrete semiconductor element 8 is connected to the inner lead 39 by means of the Au wire 9, then the circuit is sealed with resin by using an independent die for each discrete semiconductor element 8, with the lead being cut off the lead frame 41 thereby to fabricate the discrete semiconductor device (FIG. 27).
When packaging the discrete semiconductor device on a mother board, there has been such a problem that a large packaging area is required to connect the device to the mother board by using the outer lead 40 which is installed on a side face of the package and extends outward.
Also because the discrete semiconductor element and the mother board are connected by means of a lead, wiring length becomes longer and causes a substantial loss in the discrete semiconductor element in high-frequency region which leads to unsatisfactory high frequency characteristics.
Moreover, because the discrete semiconductor element is sealed with a resin of low thermal conductivity, heat dissipation efficiency decreases and causes such a problem that it is impossible to package discrete semiconductor elements of high power.
For example, Japanese Patent Kokai Publication No. 8-236665 discloses a method of packaging electronic elements on a mother board by means of bumps provided on the back of a resin-sealed semiconductor device which carries an IC chip mounted thereon, without using leads.
However, because the discrete semiconductor element employs a high power element such as power MOS device compared to an IC which employs a low power element, heat transfer through the bumps is not enough to dissipate the heat generated by the semiconductor device and the like. Also when high-frequency elements are used, it has been necessary to improve the high-frequency characteristics by making the distance between the electrode of the high-frequency element and the mother board whereon the high-frequency element is mounted as short as possible.
Moreover, in the process of producing resin-sealed discrete semiconductor devices of the prior art, semiconductor elements are sealed with resin by using an independent die for each discrete semiconductor device and injecting the sealing resin in each die, although such a method requires it to fu fabricate a new die every time the external dimension or profile of the semiconductor divide is changed, thus making it difficult to reduce the period of time and cost of development of the semiconductor devices.
Also when a lead frame is used, peripheral portion of the frame except for the leads becomes unnecessary making it difficult to reduce the producing cost.
The present invention is intended to solve the problems with the discrete semiconductor elements described above, and an object of the present invention is to provide a discrete semiconductor device which requires a small packaging area and has excellent high-frequency characteristics and good heat dissipation performance, and a method of producing the same.
The present inventors have intensively studied. As a result, the present inventors have found that it is possible to connect the back faces of die bond pads and wire bond pads directly on a mother board and to achieve the object described above, by using a discrete semiconductor device made by mounting the discrete semiconductor elements on the die bond pads and the wire bond pads and sealing the packaging surface with a resin Thus, the present invention has been accomplished.
Hence the present invention provides a discrete semiconductor device comprising die bond pads and wire bond pads arranged at specified intervals, discrete semiconductor elements which are fastened on the back face thereof onto the die bond pads and have electrodes electrically connected to the wire bond pads, and a sealing resin provided on one side of the die bond pads and the wire bond pads thereby to seal the discrete semiconductor elements.
In the discrete semiconductor device as described above, one side of the discrete semiconductor device is not sealed with resin and the die bond pads and the wire bond pads on the back side which is not sealed with the resin allow direct connection with the mother board.
Therefore, firstly, packaging area can be reduced compared to the packaging technique of the prior art which uses leads, because the discrete semiconductor device has connecting points on the back. Also because the die bond pads and the wire bond pads provided on the back can be directly connected to the mother board by using solder or the like, packaging height can also be reduced compared to the configuration of the prior art which uses bumps.
Secondly, because the discrete semiconductor elements are directly fastened on the die bond pads while the die bond pads are connected directly to the mother board, efficiency of heat dissipation of the discrete semiconductor elements can be greatly improved compared to the configuration of the prior art which dissipates heat through the leads. This configuration makes it possible to use elements which generate much heat such as power MOS devices.
Thirdly, because the die bond pads and the wire bond pads are connected directly to the mother board, connection distance between the discrete semiconductor device and the mother board can be reduced, thereby making it possible to improve the high-frequency characteristics when the discrete semiconductor device is used in a high frequency band.
Also the present invention provides a discrete semiconductor device wherein the die bond pads and the wire bond pads are electrically conductive metal sheets which are fastened at specified positions on the back of an insulating sheet and have aperture in the insulating sheet on the metal sheets, and the sealing resin is provided on one side of the die bond pads and the wire bond pads thereby to seal the discrete semiconductor element.
This makes it easy to product a plurality of semiconductor devices at the same time.
Also the present invention provides a discrete. semiconductor device wherein the die bond pads and the wire bond pads are the metal sheets which are cut off as born by the sealing resin that is formed on an electrically conductive metal sheet, and the sealing resin is provided on one side of the die bond pads and the wire bond pads thereby to fasten the die bond pads and the wire bond pads at specified intervals and seal the discrete semiconductor element.
By using the metal sheets formed at the specified intervals as the die bond pad and the wire bond pads as described above, it is made possible to manufacture the discrete semiconductor device having a plurality of semiconductor elements connected in series or parallel, having such a configuration as the wire bond pads are used in common.
The discrete semiconductor device preferably has electrodes on the back thereof and is electrically connected with the wire bond pads.
This is because the efficiency of heat dissipation can be improved and the wiring can be made shorter by fastening the discrete semiconductor element which has back side electrode directly on the conductive wire bond pad.
The discrete semiconductor element is preferably a diode or a transistor, and the metal sheet is preferably made of copper which has good electric conductivity and high heat conductivity.
The present invention also provides a discrete semiconductor device made by sealing the plurality of discrete semiconductor elements with the integral sealing resin.
The plurality of discrete semiconductor elements, having the die bond pads and/or the wire bond pads in common, are sealed with the integral resin by us.
This makes it possible to obtain the discrete semiconductor device of such a configuration as the discrete semiconductor elements are connected in series or parallel and are integrally sealed with the resin.
The present invention also provides a method for producing a discrete semiconductor device, comprising a step of forming the plurality of sets of die bond pad and wire bond pads by fastening electrically conductive metal sheets at specified positions on the back of an insulating sheet and making apertures in the insulating sheet on the metal sheets, a packaging step for fastening the back of the discrete semiconductor elements on the die bond pads and electrically connecting the electrodes of the discrete semiconductor elements and the wire bond pads, a step of sealing the plurality of the discrete semiconductor elements installed on the insulating sheet with an integral sealing resin by sealing the packaging surface of the insulating sheet with the resin, and a step of dividing the sealing resin into the discrete semiconductor devices by cutting off the sealing resin around the discrete semiconductor elements.
By employing such a producing method, use of a resin-sealing die for each discrete semiconductor device as in the prior art becomes unnecessary because a plurality of discrete semiconductor elements installed on the insulating sheet are sealed with an integral resin by using one die and then cut off to make the discrete semiconductor devices.
Therefore, when the dimension or profile of the discrete semiconductor element to be packaged is changed, profile of the sealing resin can be changed only by changing the position of cutting the sealing resin without changing the die.
With this method, period of time required for developing the discrete semiconductor device can be reduced and the developing cost can be reduced, of which effects become even more significant for discrete semiconductor devices which must be made in large variety, small lot production.
The producing cost can also be reduced because there is no unnecessary lead frame unlike in the case where lead frame is used.
The packaging step described above may also include a step of fastening the back side electrode of the discrete semiconductor device onto the die bond pad to electrically connect the die bond pad and the back side electrode.
The dividing step may also be a step of cutting off the sealing resin around a plurality of discrete semiconductor elements grouped as a single body, to obtain the discrete semiconductor device wherein the plurality of discrete semiconductor elements are sealed with the integral resin.
Such a step makes it possible to easily manufacture the discrete semiconductor device of such a configuration as the plurality of discrete semiconductor elements are sealed with the integral resin.
The present invention also provides a method for producing a discrete semiconductor device, comprising a packaging step wherein a plurality of discrete semiconductor elements are fastened, on the back thereof, onto an electrically conductive metal sheet and an electrode of each discrete semiconductor element is electrically connected to a specified position of the metal sheet, a step of sealing the packaging surface of the metal sheet with an integral sealing resin, a cut-off step of cutting off the metal sheet by cutting therein from the back thereby to turn the metal sheet into die bond pads and wire bond pads which are arranged at intervals, and a step of dividing the discrete semiconductor devices by cutting off the sealing resin around the discrete semiconductor elements.
With such a method, it is made possible change the profile of the sealing resin simply by changing the position of cutting off the sealing resin without changing the sealing die even when the dimensions or profile of the discrete semiconductor elements to be packaged is changed, and also to easily obtain the discrete semiconductor device of such a configuration as the discrete semiconductor elements are connected in series or parallel and are sealed with the integral resin.
The packaging step may also include a step of fastening the back electrode of the discrete semiconductor elements onto the metal sheet and electrically connecting the metal sheet and the back electrode.
The dividing step may also be a step of cutting off the sealing resin around a plurality of discrete semiconductor elements grouped as a single body, to divide the discrete semiconductor devices each carrying the plurality of discrete semiconductor elements being sealed with the integral resin.
Such a step makes it possible to easily obtain the discrete semiconductor device wherein the plurality of discrete semiconductor elements are sealed with the integral resin, without changing the resin-sealing die.
The cut-off step may also be a step of cutting off the metal sheet in such a way as the die bond pads and/or the wire bond pads connected to the plurality of discrete semiconductor elements become an integral body, and the dividing step may also be a step off cutting off the sealing resin around the discrete semiconductor elements which are formed so that the die bond pads and/or the wire bond pads connected to the plurality of discrete semiconductor elements become an integral body, thereby to obtain the discrete semiconductor device wherein the plurality of discrete semiconductor elements which share the die bond pads and/or the wire bond pads in common are sealed with the integral resin.
Such a method makes it possible to easily obtain the discrete semiconductor device of such a configuration as the plurality of discrete semiconductor elements are connected in series or parallel and are sealed with resin as an integral body, without changing the resin-sealing die.